id: tb Flashcards
mycobacterium tuberculosis
obligate aerobic, slow-growing, acid-fast bacilli
waxy cell membrane: does not produce a typical gram-stain response (requires acid-fast stain to visualise)
risk factors for latent and active tb
- residents of prisons, homeless shelters, nursing homes
- close contact with pulmonary tb pt
- co-infection with hiv
risk factors for active tb
- children<2yo
- elderly>65yo
- malnutrition
- immunosuppression
- co-infection with hiv
s/sx of tb
- productive cough
- hemoptysis
- fever
- fatigue
- night sweats
- weight loss
radiological findings for tb
infiltrates in the apical region, cavitary lesions
pneumonia vs tb, in terms of clinical presentation
tb gradual onset (over weeks-months) vs pneumonia acute onset (over hours-days)
tb infiltrates in the apical region vs pneumonia in the middle/lower lobes
indication for latent tb infection screening
high-risk group and intent to treat if pos:
- children with recent tb contact
- hiv-infected indiv
- pt considered for tumor necrosis factor antagonist therapy
- transplant pt
- dialysis pt
latent tb diagnosis tests
- tuberculin skin test
- interferon-gamma release assay
tuberculin skin test: pros and cons
+ high sensitivity (95-98%)
+ low cost
+ no need to collect blood samples
- false neg: immunocompromised
- false pos: envi contact w non-tb mycobacteria, bcg vaxx
- no universally accepted standards for interpreting results
- inter-reader variability
interferon-gamma release assay: pros and cons
+ performance as good as PPD
+ no false pos in bcg-vaxx indiv
+ minimal cross-reactivity with non-tb mycobacteria
+ results avail within few hrs
- more ex
- need for blood samples
- false neg: immunocompromised
most sg residents are bcg-vaxx: positive tuberculin skin tests >=
10mm
prior to treatment for latent tb
exclude active tb
latent tb treatment regimen: isoniazid
5mg/kg/d
max 300mg daily
x6mths or 9mths(hiv)
- preferred regimen, especially in pregnancy/lactation/hiv
- co-adm with pyridoxine (at least 10mg/d) to minimise neuropathy
isoniazid must be co-adm with
pyridoxine (at least 10mg/d) to minimise neuropathy(b6 deficiency)
latent tb treatment regimen: rifampicin
10mg/kg/d
max 600mg daily
x4mths
- alt in pt who cannot tolerate isoniazid
latent tb treatment regimen: isoniazid + rifapentin
900mg PO weekly
x12wk
- must be given under DOT
- not recommended for hiv pt
- limited clinical experience and evidence to date
standard 6 month active tb treatment
intensive phase: 2 months
- daily: RIPE/STM
continuation phase: 4 months
- daily or 3x/wk adm: RI
culture neg
does not imply that pt does not have tb
- mycobacterium tb is difficult to grow on culture
pyrazinamide
15-30mg/kg daily
max 2g
500mg tab
ethambutol
15-25mg/kg/d
max 1.6g
100,400mg tablet
streptomycin
IM 10-15mg/kg daily
max 1g
rifampicin
10mg/kg/d or 3x/wk
max 600mg
100,300mg tab
isoniazid
5mg/kg/d, max 300mg
15mg/kg 3x/week, max 900mg
150,300mg tab
tb drugs that req renal dose adj
P,E,STM
if unlikely to tolerate PZA eg. elderly or liver disease
standard 9-month:
- intensive phase, 2 months, daily RIE
- continuation phase, 7mths, daily or 3x/week RI
tb meds exhibit
conc-dependent killing > once-daily
risk factor for hepatotoxicity
- age>35yo
- female
- underlying liver disease
- concurrent alcohol use
- hiv
sx of hepatotoxicity
- n/v
- abdominal discomfort or pain
- unexplained fatigue
if have risk factor for hepatotoxicity, lft monitoring
at baseline and every 2-4 weeks
hepatotoxicity development
ALT>3xULN w sx or ALT>5xULN wo sx
if hepatotoxicity develops in latent tb tx
- stop tx imm
- monitor lfts
- rechallenge with inh when alt improves to <2xULN
- if pt cannot tolerate inh, switch to rifx4mths
if hepatotoxicity develops in active tb treatment
- stop tx imm
- monitor lfts
- rechallenge sequentially when lfts normalised and sx resolved
- if re-challenge fails, may need non-hepatotoxic regimen eg. ETM+FQ+STM
EMB can cause
visual toxicity
- reduced visual acuity
- reduced red-green colour discrimination
monitor visual acuity and colour discrimination test:
- at baseline for all pt
- monthly in pt w any 2 risk factors: taking etm >2 months, has renal insufficiency eg ckd
treatment of tb needs to be prolonged to ensure
killing of these slowly growing/semi-dormant org
- if not fully eradicated, might cause relapse
for active tb treatment, pt’s ___ should be documented at each visit
weight, and have drug dosages adj accordingly
adr of RIP
gi: anorexia, nausea, abdominal discomfort
- to adm after a light meal or before bedtime
- exclude hepatotoxicity if sx sevre and persisitent
adr of all first line anti-tb drugs
cutaneous reactions: pruritis - self-limiting
as a precaution, rfiampicin should be given with ____ to mothers and neonates born to monthers who have been under treatment w rifmapicin
vit K, avoid postpartum hemorrhage
(adr a/w rifampicin is thrombocytopenia)
isoniazid metabolism
in the liver, through acetylation by N-acetyltransferase
- acetylation rate related to genetic polymorphism: certain pt eg chinese in sg: rapid acetylator phenotype vs indians (slow)
isoniazid should not be taken concomittantly with foods
rich in tyramine and histamine:
- certain types of fish (tuna)
- cheese and red wine
may give rise to SE such as flushing and headache
isoniazid/etm and antacids
antacids incr gastric pH and delay absorption of isoniazid/etm - separate from isoniazid/etm ingestion by 2 hrs
isoniazid ddi
may incr conc of anticonvulsants eg phenytoin and oral anticoagulants
which anti-tb drug most effective in eliminating persisters?
pyrazinamide
pyrazinamide and gout-like sx
pyrazinoic acid, principal metabolite of pyrazinamide, inhibits renal tubular secretion of uric acid and results in gout-like sx
ethambutol and gout
reduce excretion of uric acid by kidney
adr of streptomycin
ototoxicity, neurotoxicity, nephrotoxicity
cure
neg sputum smear or culture in last month of tx and on at least one prev occasion
tx failure
pos sputum bacteriology at or after 5 months of treatment
non-conversion of sputum cultures at __ months is a good surrogate marker for risk of relapse
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